1. Field of the Invention
The present invention relates to an electrolyte membrane for a fuel cell including a blend of polymers with different degrees of sulfonation, a membrane-electrode assembly including the electrolyte membrane, and a fuel cell including the electrolyte membrane.
2. Description of the Related Art
Polymer electrolyte fuel cells (PEFCs) developed hitherto have employed Nafion membranes, which are perfluorosulfonated polymer membranes produced by DuPont, as electrolyte membranes. However, Nafion membranes are not attractive from the viewpoint of industrial application due to their high prices. Another disadvantage of Nafion membranes is high fuel permeability. Under such circumstances, a great deal of research has been conducted on electrolyte membranes using hydrocarbon polymers.
Generally, hydrocarbon polymer electrolyte membranes have better barrier properties and can be produced at lower cost than perfluorosulfonated polymer membranes, but have disadvantages of relatively high water solubility and poor dimensional stability, making it impossible to provide long-term stability comparable to that of perfluorosulfonated polymer membranes. Due to these disadvantages, attempts to commercialize perfluorosulfonated polymer membranes have not yet been successful.